1. Field of the Invention
The present invention is directed to a new class of polyhydroxypolyamides and a process for making same. More specifically, the present invention is directed to a class of polyhydroxypolyamides derived from aldose sugars and a process for forming said polymers.
2. Background of the Prior Art
Carbohydrate polymers are generally associated with that class of highly functionalized naturally occurring materials known as polysaccharides. Polysaccharides are an extremely important class of polymers due to their wide natural occurrence, their importance in health and nutrition and their wide use in agricultural, food, textile, pharmaceutical and paper industries. These polymers are formed from cyclic monosaccharide units which are linked by glycosidic (acetal) bonds. Naturally occurring monosaccharides, with their variance in carbon chain length and stereochemistry, also offer great potential as starting materials for the synthesis of carbohydrate polymers other than polysaccharides, specifically acyclic polymers with carbohydrates as part of the chain or as pendant groups.
The potential for producing synthetic polymers based on carbohydrates is a concept known in the art. Nylon-type polyamides, polymethacrylates and polyesters derived from hydroxyl protected carbohydrates have been prepared.
In the formation of synthetic polyamides from carbohydrates dialkyl aldarates have been condensed with amines to prepare polyamides. Ogata et al., J. Polym. Sci: Polym. Chem. Ed., 14, 783 (1976) describes a condensation copolymerization between diethyl galactarate and hexamethylene diamine to form a nylon type polyamide. This polymerization occurs in a moderately polar to polar solvent such as dioxane, tetrahydrofuran, dimethylformamide, acetonitrile, ethylene glycol, dimethyl acetamide, methanol or methyl sulfoxide. In the solution polymerization reaction the polyamide product precipitates as a solid directly from the reaction mixture. A similar copolymerization, between diethyl galactarate and ethylene diamine, was more recently reported by Hoagland, P. D. Hoagland, Carbohydrate Res. 98, 203 (1981).
The Ogata et al. and Hoagland teachings represent an advance in the art. However, these disclosures are limited by the requirement that a pure diester, prepared from a pure diacid, be available as a starting reactant. Those skilled in the art are aware that such a process is not commercial. With the exception of galactose, none of the commercially available aldose sugar diacids form pure aldarates (diesters) in the well known Fischer esterification reaction. For this reason there has been no attempt to commercialize this process, albeit, the polymer product of this reaction has utility. As such there is similarly no teaching in the prior art directed to the copolymer product of this process, a polyhydroxypolyamide, other than the above-discussed galactarate copolyamides.
The above remarks establish the desirability of developing a new process which results in the formation of a polyhydroxypolyamide from a readily available and low cost monosaccharide. That is, it is clear that if a process to produce polyhydroxypolyamides from low cost monosaccharides without the almost impossible task of having to prepare and purify diester derivatives thereof could be found, a whole new and useful class of polymers could be developed.
Polyhydroxypolyamides, derived from carbohydrates, have many developing applications: as textiles, in the production of safety glass, as adhesives, as water-based emulsion paints, as fibers and in the formation of durable structural plastics. These polymers are additionally of interest as precursors for polymeric bases, as metal complexing agents, as precursors for polyelectrolytes and as pharmaceutical complexing agents. Furthermore, because of their alternating hydrophobic and hydrophilic monomeric units, these polymers and derivatives thereof possess liquid crystal properties, properties that are important in the formation of high tensile strength fibers.